Reinsurance Reinsurance (Ceded Reinsurance Receivable Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 983	$ 904
Reinsurance Recoverables, Percentage of Total	100.00%	100.00%
Other Reinsurers [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 182	$ 149
Reinsurance Recoverables, Percentage of Total	18.50%	16.40%
AM Best, A+ Rating [Member] | Reinsurer A [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 420	$ 367
Reinsurance Recoverables, Percentage of Total	42.70%	40.60%
AM Best, A+ Rating [Member] | Reinsurer B [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 216	$ 208
Reinsurance Recoverables, Percentage of Total	22.00%	23.00%
AM Best, A+ Rating [Member] | Reinsurer D [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 55	$ 53
Reinsurance Recoverables, Percentage of Total	5.60%	5.90%
AM Best, A Rating [Member] | Reinsurer C [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 64	$ 84
Reinsurance Recoverables, Percentage of Total	6.50%	9.30%
AM Best, A++ Rating [Member] | Reinsurer E [Member]
Ceded Credit Risk [Line Items]
Reinsurance ceded receivables	$ 46	$ 43
Reinsurance Recoverables, Percentage of Total	4.70%	4.80%